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AOCS Design Upgrade Based On Operator Needs And Emerging Sensors

Objectives

The objectives of this study are:

On one hand, to take benefit on the telecommunications satellites from the availability of recently developed sensors and actuators to determine at system level how the AOCS could handle new functions or decrease its cost.

On the other hand, to analyse the new requirements of the operators induced by the increased number of collocated spacecraft or the recent issue of the French law about space activity.

Challenges

With this study, Thales Alenia Space has continued to improve the common Spacebus/Alphabus AOCS with very challenging cost competitiveness objectives while improving the functionality offered to the operators.

The decrease of the AOCS cost has been made possible thanks to the introduction of low cost sensors like the Sun sensor on a chip or the micro-gyro. For this new low cost coarse gyro, the challenge has been to adapt of the existing AOCS to the loss of performance of this sensor.

The compliance of the common Spacebus/Alphabus AOCS to the new requirements of the operators have been also challenging.

It has required the design of a Gyro-less AOCS which permit without any over cost to operate and deorbited a spacecraft even with two gyros failed.

The optimisation of the electrical propulsion with a new three axis deployable and pointing mechanism has also been required to offer larger platforms while improving the competitiveness of the common Spacebus/Alphabus avionics.

Benefits

The objective for THALES ALENIA Space is to anticipate attitude control emerging sensor and operator need and, thus, to improve its competitiveness and offer better service to its customers.

The benefit expected for THALES ALENIA Space is to offer on the market as soon as 2014 an improved version of its SPACEBUS 4000 attitude and orbit control (AOCS).

Features

Thanks to the innovations and progresses recently performed in micro-engineering, new technologies have emerged and found promising use in space.

The sun sensors benefit of these developments based on CMOS technology, notably Active Pixel Sensor photo detector (APS), which permits to integrate the electronics, and the detector on a same chip. During this study, the introduction of a sun sensor on a chip (SSoC) developed by SELEX with ESA support and the benefits allowed by this cheap and simple sensor have been analysed.

The Gyro-meters also benefit of these developments based on Nano technology, like Microelectromechanical systems (MEMS) Gyro-meters, which permit to miniaturize the angular rate sensors. However this miniaturization is associated with a loss of performance due to an increase of bias, drift and noise. In the frame of this study, the AOCS has been adapted for less stringent rate sensor specification in order to envision cheaper equipment like micro-gyro.

This Study has also permit to analyse the new requirements of the operators through the development of a Gyro-less AOCS to offer the capability of the common Spacebus/Alphabus avionics to operate and re-orbit the S/C in case of failure of both gyros.

Furthermore this study has permit to prepare the optimization of the electrical propulsion with a three axis deployable and pointing mechanism to reduce the chemical pulse number in order to envision different thruster providers and to offer larger platforms with the electrical propulsion.

Plan

This study started from the existing SPACEBUS/ALPHABUS common AOCS in 2012, and end up with the development, software prototyping and validation tests of the selected new functions in 2014.

Current status

All activities are now fully completed.

The Sun sensor on a chip (SSoC) which could ease the sun sensor accommodation and improve the sun detection, has been accommodated on a Spacebus 4000 and several benefits have been analysed.

The Spacebus 4000 AOCS has been modified to be compliant to The Micro-electromechanical systems (MEMS) Gyro-meters recently developed that could decrease the cost of the Attitude and orbit control sub-system. Software modifications have been validated with a prototype on board software on a Hi-Fi simulator.

The development of a Gyro-less AOCS, to offer the capability of the common Spacebus/Alphabus avionics to operate and re-orbit the S/C in case of failure of both gyros, has been validated with a prototype on board software on a Hi-Fi simulator

The optimization of the electrical propulsion with a three axis deployable and pointing mechanism to reduce the chemical pulse number in order to offer larger platforms with the electrical propulsion has been performed. A combined Station keeping and angular momentum control strategy has been design and the three axis arm control law has been validated on a Hi-Fi simulator.